1. Field of the Invention
The present invention relates to a launching and/or receiving network for an antenna system and, more particularly to a launching and/or receiving network for a microwave antenna system which is capable of launching signals in a first frequency band through a feedhorn of, for example, an existing antenna system without perturbing the transmission of signals in other frequency bands also being launched in the feedhorn.
2. Description of the Prior Art
Present telecommunication microwave radio systems generally transmit signals in the frequency bands of 4, 6 and 11 GHz. In multiplexing or demultiplexing the individual frequency bands for transmission by a directive antenna system, prior art systems have used various waveguide elements in the transmission line to the feedhorn such as Y-junctions, directional couplers, polarization separator-mixers and predistorted microwave filters in branching networks. In this regard see, for instance, U.S. Pat. Nos. 3,543,188 issued to R. M. Livingston on Nov. 24, 1970; 3,816,835 issued to N. Bui-Hai et al on June 11, 1974 and 3,943,519 issued to N. Bui-Hai on Mar. 9, 1976.
Where frequency bands other than the three 4, 6 and 11 GHz frequency bands are to be transmitted over a single antenna system and where these other frequency bands are not supportable by the waveguide transmission line used for the 4, 6 and 11 GHz signals, prior art arrangements have generally used a separate waveguide transmission line and feedhorn for launching and receiving the other frequency bands directly to and from a reflector. In this regard see, for instance, U.S. Pat. No. 3,763,493 issued to S. Shimada et al on Oct. 2, 1973.
Under certain conditions, however, it may not be possible to add a separate feedhorn such as, for example, in the throat of a horn-reflector antenna, and especially when it is desired to add a new frequency band to an existing microwave telecommunication system, which new frequency band is not supportable by the existing waveguide connected to the feedhorn. The problem, therefore, remaining in the art is to provide an arrangement for launching and/or receiving electromagnetic waves in a first frequency band through a feedhorn which is used to launch and/or receive electromagnetic waves in one or more other frequency bands without perturbing these latter other frequency band signals.